US newspapers big and small hit back Thursday at Donald Trump's attacks on the news media with a coordinated campaign of editorials, triggering a fresh tirade from the president on Twitter.

Leading the charge was The Boston Globe, which had called for the drive highlighting the importance of a free press, accompanied by the hashtag #EnemyOfNone.

More than 300 newspapers around the country joined the effort.

"Today in the United States we have a president who has created a mantra that members of the media who do not blatantly support the policies of the current US administration are the 'enemy of the people,'" the Globe editorial said.

"This is one of the many lies that have been thrown out by this president, much like an old-time charlatan threw out 'magic' dust or water on a hopeful crowd," it added in a piece entitled "Journalists are not the Enemy."

The effort comes amid Trump's persistent claims that mainstream media outlets that publish articles critical of him are churning out "fake news."

The New York Times, a frequent target of Trump's criticism, ran a seven-paragraph editorial under a giant headline with all capital letters that read "A FREE PRESS NEEDS YOU."

"Insisting that truths you don't like are 'fake news' is dangerous to the lifeblood of democracy. And calling journalists the 'enemy of the people' is dangerous, period," the Times wrote.

Trump fired back on Twitter by repeating his contention that the "fake" news media is "the opposition party" and claiming the Boston Globe was "in collusion" against him with other media.

"There is nothing that I would want more for our Country than true FREEDOM OF THE PRESS," he tweeted.

"The fact is that the Press is FREE to write and say anything it wants, but much of what it says is FAKE NEWS, pushing a political agenda or just plain trying to hurt people."

The US Senate meanwhile countered the White House by unanimously passing a resolution citing the "indispensable role of the free press" and warning that efforts to undermine the media were "an attack on our democratic institutions."

Other newspapers joining the campaign said Trump's attacks diminish the importance of journalists in their communities.

"For more than two centuries.. the press has served as a check on power, informing the American people about corruption and greed, triumphs and tragedies, grave mistakes and misdeeds and even ineptitude and dysfunction," wrote the Albuquerque Journal in New Mexico.

Iowa's Des Moines Register said, "The true enemies of the people -- and democracy -- are those who try to suffocate truth by vilifying and demonizing the messenger."

- Cannot sit back -

Free press advocates argue that Trump's attacks imperil the constitutional First Amendment guarantee of freedom of the press.

"I don't think the press can just sit back and take it, they need to make their case when the most powerful man in the world tries to undercut the First Amendment," said Ken Paulson, a former editor-in-chief of USA Today who is dean of communications at Middle Tennessee State University.

But Paulson questioned whether editorials would be effective.

"The people who read editorials don’t need to be convinced," he said. "They are not the ones trying to shout you down at presidential rallies."

The campaign also faced the potential for galvanizing supporters of the president around the notion that the media is out to get him.

The San Francisco Chronicle said it would not join the effort because "it plays into Trump's narrative that the media are aligned against him."

But the newspaper said it would "continue to speak out against this president's war on the free press," doing it "in our own way, on our own timetable."

- Stakes too high -

But media rights advocates say the stakes are too high to allow the president's claims to go unchecked.

Some say Trump's comments have incited threats against journalists covering his events, and may have created a climate of hostility that opened the door to violent attacks like a deadly one in June against the Capital Gazette in Annapolis, Maryland.

"Trump's references to us as the 'enemy of the American People' are no less dangerous because they happen to be strategic," the Kansas City Star wrote. "That is what Nazis called Jews. It's how Joseph Stalin's critics were marked for execution."

Trump's actions are also encouraging strongmen such as Vladimir Putin of Russia and Recep Tayyip Erdogan in Turkey to treat journalists like enemies, some newspapers said.

"The messages in today's newspapers are best read not as a drift toward war footing, but rather as a reminder that journalism is important work," wrote Pete Vernon in the Columbia Journalism Review.